Several observations concerning 6:1, the thesis statement for this section, are appropriate before we approach the following paragraphs of the passage in more detail.
First, we must impress God alone. In all three examples Jesus warns his followers not to be like the hypocrites (6:2, 5, 16; also 15:7; 22:18; 23:13-29; 24:51). This term originally designated actors in the theater, though both Greek and Jewish texts had long before come to apply it figuratively.
One of human religion's greatest temptations is to act piously to elicit the praise of others. A secret atheist could practice religion in that form without the slightest element of faith (compare 23:5). Such temptations were part and parcel of ancient religion; for instance, when some first-century Jewish leaders called a fast for unrighteous reasons, others feared not to observe it, lest anyone question their piety (Jos. Life 290-91). Yet the same temptation is no less real today. Jesus reminds us that true piety means impressing God alone-living our lives in the recognition that God knows every thought and deed, and it is his approval alone that matters. Matthew again praises the meek, whose only hope is in God, not in others' opinions of them. Those of us who are "religious professionals," making our living from public ministry, should take special heed: if we value the approval or pay of our congregations more than what God has called us to do, we will have no reward left when we stand before him.
Second, Jesus' warning does not preclude public acts of righteousness. Public righteousness, even when carried out in the knowledge that such acts will draw attention, is not wrong so long as we seek to be seen for God's glory rather than our own (5:16). This text warns us, however, how easy it is to justify our own desire to impress others as "being a light." We should do everything for God (Rom 14:6-8; 1 Cor 10:31; Col 3:17); the repentant person who lives in view of the coming kingdom (4:17) is concerned more with God's evaluation than with that of others. Many people practice religion without paying attention to God, and this warns us to search our motives.
Third, Jesus demands practice, not just theory. Jesus' Jewish contemporaries agreed with most of what he was teaching here (ARN 28A; 40A; 46, 129B). Thus Jesus is not satisfied that we claim to agree with his ethics; he wants us to live accordingly.
Fourth, Jesus' three examples are random, so secrecy must apply to all acts of righteousness. Judaism often listed righteous works, sometimes in sets of threes (Jesus' list here resembles Tobit 12:8), but such lists were never more than random examples. We must thus apply Jesus' principle to all our acts of righteousness.
Fifth, Jesus promises eternal reward for those who seek to please God rather than mortals. Jesus concludes his warnings with another graphic image: businessmen regularly wrote the phrase received their reward in full (see 6:2, 5, 16) on receipts to indicate that no further payment was required (Deissmann 1978:110). Jesus is saying that those who give charity to be admired by others, or pray and fast to people rather than to God, already have what they wanted: others' approval. They will not be rewarded again for their deeds on the day of judgment.
Finally, Jesus defines true religion differently from the way many Christians do. If it is possible to pray, fast and give alms extensively and yet do it from wrong motives, we must reevaluate our religious values. Most people I know who pray four hours a day have a very close walk with God. But I know others whose calling may allow them only an hour a day of concerted prayer, yet their walk is probably just as close to God, since they are living according to his will. We should pray, fast and serve the needy because we love God-not in order to convince anyone, including ourselves, that we do.